(1) Field of the Invention
The present invention relates to a plastics shaping mold and a method of preparing the mold, which mold is used for manufacturing plastic articles having various patterns defined by unevenness of its surface such as a wood grain pattern, an aventurine pattern and a marbled pattern. More particularly, the invention relates to a plastics shaping mold and a method of preparing the mold, which mold defines an uneven shaping surface for forming an uneven surface pattern, that is to say for manufacturing plastic articles with an uneven surface pattern.
(2) Description of the Prior Art
It has been conventional practice to etch the uneven shaping surface on a metal mold as shown in FIG. 15 of the accompanying drawings.
According to such a method, projections on the shaping surface are all of an equal height since the unevenness of the metal mold surface is formed by etching. As a result, recesses of the pattern formed on the plastic articles are all of the same depth, which fails to provide the articles with a sufficient touch of rich quality.
On the other hand, a plastics shaping mold has been proposed which has an uneven shaping surface reinforced by applying to the metal mold surface a resin layer formed of a resin impregnated with glass fiber (see the Japanese patent application laid open under No 50-34058). However, in the case of this plastics shaping mold, if it is attempted to reduce the thickness of the resin layer (to less than 0.5 mm) in order to avoid the deformation and quality deterioration due to heating by improving the heat conductivity between the resin and the mold (generally of metal) in the course of forming the plastics, since the glass fiber contained in this resin layer has a substantially long chop strand length, on the order of 2-3 mm, there tends to occur disadvantageous directional concentration of the glass fibers in this thin resin layer; that is, most of the glass fibers tend to be aligned horizontally along the shaping surface.
This horizontal concentration in the alignment of the glass fibers results in vulnerability of the resin layer against the heat or external physical forces. Moreover, the above-described relatively long length (2-3 mm) of the glass fiber also caused difficulty in accurately forming a very fine concave-convex pattern in the resin.
Furthermore, a mold for injection molding has been developed as the plastics shaping mold having uneven surfaces, which utilizes an epoxy resin (trade name: ARARUDITE which is an epoxy resin adhesive agent). This plastics shaping mold comprises an upper and a lower jaws formed of cast aluminum and each carrying an ARARUDITE layer having a fixed thickness (2-3 mm) coated over an entire surface thereof. Plastic articles are obtained by injecting resin into a space between the upper and lower jaws.
With this plastics shaping mold, however, the resin covering the shaping surfaces has only insufficient strength and has a short life of use since the resin covers the entire surfaces. After all, this mold serves just as a simplified version of mold not capable of withstanding an increased production.